rata around volcanic
vents (which has since been confirmed by Mr Heaphy in New Zealand and
other authors) awakened an intense enthusiasm, and he writes: "It then
first dawned on me that I might perhaps write a book on the geology of
the various countries visited, and this made me thrill with delight.
That was a memorable hour to me, and how distinctly I can call to mind
the low cliff of lava beneath which I rested, with the sun glaring hot,
a few strange desert plants growing near, and with living corals in the
tidal pools at my feet." ("L.L." I. page 66.)

But it was when the "Beagle", after touching at St Paul's rock and
Tristan d'Acunha (for a sufficient time only to collect specimens),
reached the shores of South America, that Darwin's real work began; and
he was able, while the marine surveys were in progress, to make many
extensive journeys on land. His letters at this time show that geology
had become his chief delight, and such exclamations as "Geology carries
the day," "I find in Geology a never failing interest," etc. abound in
his correspondence.

Darwin's time was divided between the study of the great deposits of red
mud--the Pampean formation--with its interesting fossil bones and shells
affording proofs of slow and constant movements of the land, and the
underlying masses of metamorphic and plutonic rocks. Writing to Henslow
in March, 1834, he says: "I am quite charmed with Geology, but, like
the wise animal between two bundles of hay, I do not know which to
like best; the old crystalline groups of rocks, or the softer and
fossiliferous beds. When puzzling about stratification, etc., I
feel inclined to cry 'a fig for your big oysters, and your bigger
megatheriums.' But then when digging out some fine bones, I wonder how
any man can tire his arms with hammering granite." ("L.L." I. page
249.) We are told by Darwin that he loved to reason about and attempt to
predict the nature of the rocks in each new district before he arrived
at it.

This love of guessing as to the geology of a district he was about to
visit is amusingly expressed by him in a letter (of May, 1832) to his
cousin and old college-friend, Fox. After alluding to the beetles he
had been collecting--a taste his friend had in common with himself--he
writes of geology that "It is like the pleasure of gambling. Speculating
on first arriving, what the rocks may be, I often mentally cry out 3 to
1 tertiary against primitive; but the latter have h